The present disclosure generally relates to relates to an ambulatory infusion device comprising a replaceable energy storage and a method of monitoring a replaceable energy storage of a medical device and, in particular, to an ambulatory infusion device which comprises a replaceable energy storage for electrically powering several functional units of the device and a measuring module configured to measure the voltage of the energy storage.
Medical devices are required to comply with strict requirements concerning availability and reliable power supply. Specifically, for medical devices such as external ambulatory infusion devices, regulatory requirements demand secure monitoring of energy cells that are used to power the device and signaling in good time to the user when the energy cell is expected to be depleted.
External ambulatory infusion devices for the infusion of a liquid drug over an extended time period are known in the art for a number of therapies. In particular, such devices form the basis for a state-of-the-art therapy of Diabetes Mellitus by CSII (Continuous Subcutaneous Insulin Infusion). Besides diabetes therapy, these devices may be used for a number of further therapies, such as cancer treatment or pain therapy, without requiring substantial modification.
Typically, these devices are powered by user-replaceable energy storage, particularly, by one or more energy cells including rechargeable and non-rechargeable batteries. For the batteries, distinct performance characteristics are generally required for safe and reliable operation. Therefore, some devices are powered by special-purpose power packs which are especially designed to meet device requirements. This approach, however, is accompanied by some drawbacks. In particular, the user has to stock the power packs and carry a number of them, for example when traveling. In addition, the price of the power packs is high because of the comparatively low production volumes.
Some other devices are therefore designed to be powered by widely available, conventional batteries, such as AA or AAA cells. Such standard batteries have no proprietary and/or device-specific features or built-in energy/charge-monitoring systems. Consequently, in order to adhere to regulatory requirements, such medical devices must be configured to monitor the energy/charge of such standard batteries. Accordingly, state-of-the-art devices perform battery tests by connecting the battery terminals periodically to a given test load, for stressing the battery with a defined stress test, and measuring the corresponding terminal voltage. An alert is generated when the measured voltage is below a given threshold voltage. The testing interval between consecutive tests is typically in the range of some minutes. However, standard batteries come in a variety of different electrochemical designs and electrical behavior, and thus a device may spontaneously terminate operation without alerting the user, when the battery's voltage drops, during operation of the device, from a high level at, which no alert would be generated, to a very low level, which is no longer sufficient for operating the device, with a steep drop of the terminal voltage and within and in a short time. Because in this case, the user is not aware of the terminated infusion of the drug or substance, this may result in severe adverse effects.
Therefore, there is a need for a device and method to monitor reliably the energy of the replaceable energy storage of an ambulatory infusion device.